Preparation and analysis of lightweight wall material with expanded graphite (EG)/paraffin composites for solar energy storage

Lightweight wall material (LWM) composited with EG/paraffin composite was prepared by experimental procedures of foaming, slip casting and constant temperature curing. The EG/paraffin composites were synthesized via vacuum impregnation method. The scanning electron microscope (SEM) analysis indicated that paraffin was sufficiently absorbed into the EG porous network and depicted no leakage even in the molten state. The X-ray diffractometer (XRD) and Fourier transformation infrared spectroscope (FT-IR) results revealed that paraffin and EG in the composite didn't undergo chemical reactions but only physical combination. The compressive strength value of the sample reached 2.853 MPa, while bulk density reduced to 0.445 kg/m3. The differential scanning calorimeter (DSC) results revealed that the sample melts at 47.78 °C with a latent heat of 16.26 J/g and solidifies at 43.81 °C with a latent heat of 15.98 J/g. The sample with 15% EG/paraffin composites had adequate stability by contrasting mechanical property and DSC profiles before and after 200 times thermal cycles. Furthermore, the thermal conductivity of the LWM increased to 0.76 W (m K) when 20% EG/paraffin was added into the composite. This indicates that the prepared sample has a good thermal property. Hence, the LWM containing EG/paraffin composite would be useful as thermal energy storage material.